Pressure-sensitive adhesives (PSAs) constitute one group of adhesives and are often used in the form of PSA tape, PSA label or the like obtained by coating PSA onto a substrate and curing. Such tapes and labels are typical of PSA articles familiar in everyday life. These articles are used as labels for identification, for packing of things, for binding a plurality of parts, and in many other applications.
Several base materials are known for PSAs and generally classified into rubber, acrylic, and silicone bases. Rubber base PSAs are general-purpose base materials which are known from the past, and frequently used as general-purpose tape and other products because of low price. Acrylic base PSAs are based on polyacrylates and have better chemical properties than the rubber base PSAs, and are applicable to higher performance PSA products. Silicone base PSAs are composed of high viscosity silicone gum and silicone resin wherein the backbone is formed of siloxane bonds. Thus the silicone PSAs have a variety of excellent characteristics such as heat resistance, freeze resistance, weather resistance, chemical resistance and electric insulation.
By virtue of such excellent characteristics, the silicone PSAs are used as industrial high-performance tapes such as heat resistant tape, masking tape for processing, and flame retardant mica tape. They are often used in a rigorous environment since they exert their own characteristics even under severe service conditions.
Further, since the silicone PSAs are fully adhesive to surfaces coated with silicone rubber and silicone base materials, they are also utilized for tying silicone-treated release liners. However, the silicone base PSAs cannot be smoothly peeled from those release liners used with the acrylic and rubber base PSAs.
Under the circumstances, release agents based on fluorinated materials are used. Patent Document 1 (JP 2513026) describes a release agent based on a polymer obtained from copolymerization of a fluorinated vinyl monomer and a silicon-containing vinyl monomer. Patent Documents 2 to 6 (JP-B H05-007434, JP-B H07-051699, JP 3024445, JP 4524549, and JP 5343911) refer to release agents based on an organopolysiloxane modified with a fluorinated organic group, and describe that a cured coating obtained from hydrosilylation is formed on a substrate, which is used as a release liner. In Patent Document 6, the composition is a solventless system.
In the inventions cited above, an adhesive substrate obtained by coating and curing silicone PSA to a substrate can be readily peeled, and the silicone PSA maintains good adhesiveness even after peeling. When it is desired to adjust the release force, the release force may be altered by controlling the fluorine content of the base polymer or by changing the type of fluorinated organic group. For example, when the silicone PSA is used without a substrate, PSA on its opposed surfaces is sandwiched between releasable cured coatings and one side coating is peeled off. At this point, there must be a difference in release force between the opposed surfaces. To this end, a release agent with a low release force and a release agent with a high release force must be used.
The release force may be increased by reducing the fluorine content of the release agent, but there are no reports of increasing the release force by other means. One approach that can be contemplated is by adding an additional component to the release agent to increase the release force. If this approach is possible, there is no need to furnish two release agents having different fluorine contents in order to form cured coatings with different release forces.